Dennis,
I'm writting from Brasil, here we had for a long time this 2 engines, the 153 like the U.S. built and a 151 quite similar, but I just don't know if there is anything quite like it there.
I've assembled some 3.250" cranks into 151 engines sometimes, no big problem. Our 151 has 6.000 long rods, and the 153 has 5.700, both cranks have the very same 2.000"/2.300" journals, so no sweat here. The deal is: use the 3.250" crank, 5.700" rods and 327 Chevy V8 pistons. Or use the 6.000 rod and get a set of 350 pistons, mill the top a li'l, and you're thru. I do strongly recommend using forged pistons like trw 2403, that are stronger than the cast ones. But if You have acess to a 181, I see no point in dealing with smaller engines. The 181 head is quite superior, has non-siamesed intake ports, that may be a bonus if you may want a better milleage, it'll give a stronger pulsation in the intake, making easier to start the main circuit of the carb. The only drawback of the 181, that would make some sense using he smaller motor should be the vibes, the 181 is somewhat harsh, the 6.000 rod 151 is quite smoother.
Hope have helped.
